1. Field of the Invention
The present invention relates to a packaging structure, and more particularly, to a packaging structure for an optical sensor.
2. Description of the Prior Art
The packaging of an integrated circuit (IC) is to provide connections between the die, the packaging structure and the circuit board. The IC packaging also provides a suitable operating environment for the IC's operation. The main purposes of the IC packaging are:
(1) power transmission;
(2) signal transmission, including the external signals and the internal electronic signals;
(3) heat dissipation, including structural and material heat dissipation;
(4) circuit protection.
In addition to the above-mentioned purposes, manufacturing costs and stability of an IC package also need to be taken into considerations.
To achieve the purpose of signal transmission in a packaging design for an optical sensor, a substrate with drill holes is used in a packaging method called leadless chip carrier (LCC), as illustrated in FIG. 1. FIG. 1 is a diagram of a prior art packaging structure 100. In other common packaging methods, such as dual-in-line package (DIP) or small outline package (SOP), the pins are formed along the two sides of the die. Unlike those methods, in the LCC technology the pins are formed around the four sides of the die. Therefore the LCC technology offers more pins than DIP and SOP, usually ranging from 20 to 96 pins. To accommodate this four-sided pin layout, in the LCC technology a special substrate with drill holes formed at the four sides of the substrate is required, as illustrated in FIG. 1. These drill holes result in a substrate material usage lower than 70%, with the result that the substrate cost contributes a large part of the overall packaging cost.
Another common packaging method is called land grid array (LGA), as illustrated in FIG. 2. FIG. 2 is a diagram of another prior art packaging structure 200. In the packaging structure 200, a die 20 is coupled to a plurality of bonding fingers 14 by a plurality of gold wires 18 in a die bond process. A plurality of traces 16 are disposed on a substrate 12, coupling the bonding fingers 14 to a circuit board 24 through a plurality of vias 26 formed within a plurality of drill holes 210 for transmitting signals. In the LGA technology in FIG. 2, the plurality of drill holes 210 are made in the inner part of the substrate 12. Based on different chip designs and pin layouts, there are many types of substrates with drill holes formed in their inner parts available.
The packaging structure 100 and the packaging structure have one thing in common; that is, both packaging structures include a cavity structure 34. The packaging process of an optical sensor includes a sealing process, which is performed at an elevated temperature and which thus produces moisture. To prevent the moisture from entering the cavity structure 34 through the drill holes during the sealing process and the reliability tests, another “plug-in” process has to be included in producing the prior art packaging structures 100 and 200, which thus increases the manufacturing cost.